Cutting mechanism for a saber saw

ABSTRACT

A counterweight is provided to cancel axial vibration of a plunger of a saber saw. Swing rollers, rotatably supported at both ends of a roller shaft provided at a rear end of the plunger, interpose between a pair of opposing tracks formed in an axially elongated groove formed on the counterweight.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending application Ser.No. 09/468,127 filed on Dec. 21, 1999 now U.S. Pat. No. 6,282,797.

BACKGROUND OF THE INVENTION

The present invention relates to saber saws. Various saber saws havebeen conventionally developed to cut or saw woody or steel materials orpipes in the housing or building construction sites or similar fields.

Conventional saber saws are basically classified into first and secondtypes. According to a saber saw of the first type, a saw blade isreciprocated along a linear path. According to a saber saw of the secondtype, a saw blade is moved along an orbital path, for example, anelliptic path. The second type is also referred to as the orbitalcutting type.

U.S. Pat. No. 3,945,120 discloses a vibration dampening and heat sinkmechanism for a reciprocating hand-held saw which has a carrier guidewith limited axial and radial movement positively controlled by aneccentric.

The conventional saber saws of the orbital cutting type, for exampledisclosed in U.S. Pat. No. 3,945,120 and in U.S. Pat. No. 3,461,732, arepreferable to cut relatively soft material, such as woody members.

In general, reciprocative movement of the saber saws cause axialvibration. Providing a counterweight is effective to suppress suchvibrations (refer to U.S. Pat. Nos. 5,025,562 and 5,555,626).

SUMMARY OF THE INVENTION

An object of the present invention is to provide a saber saw of theorbital cutting type which can operate properly even when a saw blade isinversely attached to a saber saw body while suppressing vibration.

In order to accomplish this and other related objects, the presentinvention provides a first saber saw comprising a housing foraccommodating a motor. A driven shaft is rotatably supported by thehousing and rotated by the motor. A plunger causes reciprocative motionwith respect to the housing. A saw blade is attached to a front end ofthe plunger. A first motion converting mechanism, interposed between thedriven shaft and the plunger, converts rotational motion of the drivenshaft into the reciprocative motion of the plunger. A counterweightcauses reciprocative motion with respect to the housing. A second motionconverting mechanism, interposed between the driven shaft and thecounterweight, converts the rotational motion of the driven shaft intothe reciprocative motion of the counterweight. A pair of opposingtracks, formed on the counterweight, extend in a direction substantiallyparallel to a reciprocating direction of the plunger. Guide means of theplunger can reciprocate along one of the opposing tracks formed on thecounterweight while a clearance is maintained between the guide meansand the other track.

According to the first saber saw, it is preferable that a roller shaftis provided at a rear end of the plunger so as to extend in a directionnormal to the reciprocating direction of the plunger. Swing rollersserving as guide means, rotatably supported at both ends of the rollershaft, roll along one of the opposing tracks formed on thecounterweight.

Furthermore, the present invention provides a second saber sawcomprising a housing for accommodating a motor. A driven shaft isrotatably supported by the housing and rotated by the motor. A plungercauses reciprocative motion with respect to the housing. A saw blade isattached to a front end of the plunger. A guide sleeve, holding theplunger, is hingedly supported about a pivot fixed to the housing sothat the guide sleeve can swing in a direction normal to a reciprocatingdirection of the plunger. A first motion converting mechanism,interposed between the driven shaft and the plunger, converts rotationalmotion of the driven shaft into the reciprocative motion of the plunger.A counterweight causes reciprocative motion with respect to the housing.A second motion converting mechanism, interposed between the drivenshaft and the counterweight, converts the rotational motion of thedriven shaft into the reciprocative motion of the counterweight. A pairof opposing tracks, formed on the counterweight, extend in a directionsubstantially parallel to a reciprocating direction of the plunger. Theplunger can reciprocate along one of the opposing tracks formed on thecounterweight. A roller shaft is provided at a rear end of the plungerso as to extend in a direction normal to the reciprocating direction ofthe plunger. The roller shaft is inserted in an elongated hole opened onthe guide sleeve. And, swing rollers, rotatably supported at both endsof the roller shaft, roll along one of the opposing tracks formed on thecounterweight while maintaining a clearance between each roller and theother track.

According to the first and second saber saws of the present invention,it is preferable that the pair of opposing tracks are formed in anaxially elongated groove of the counterweight and the swing rollersinterpose between the opposing tracks so as to leave a predeterminedclearance. Furthermore, the swing rollers are depressed on one of theopposing tracks formed on the counterweight when the saw blade receivesa reaction force from a material to be cut during a cutting operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription which is to be read in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a side view showing a cutting operation of a saber saw;

FIG. 2 is a side view showing another cutting operation of a saber saw;

FIG. 3 is a partly cross-sectional view showing a saber saw inaccordance with a preferred embodiment of the present invention;

FIG. 4 is a cross-sectional view taken along a line A—A of FIG. 3;

FIG. 5 is a cross-sectional view taken along a line B—B of FIG. 3;

FIG. 6 is a cross-sectional view showing essential arrangement of acutting mechanism of the present invention;

FIG. 7 is a cross-sectional view taken along a line C—C of FIG. 6;

FIG. 8 is a cross-sectional view taken along a line D—D of FIG. 7;

FIG. 9 is a cross-sectional view taken along a line E—E of FIG. 7;

FIGS. 10 to 12 are views successively illustrating a linear cuttingoperation of the saber saw in accordance with the preferred embodimentof the present invention;

FIGS. 13 to 15 are views successively illustrating an orbital cuttingoperation of the saber saw in accordance with the preferred embodimentof the present invention; and

FIGS. 16 to 18 are views successively illustrating another orbitalcutting operation of the saber saw in accordance with the preferredembodiment of the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows an ordinary cutting operation of a saber saw according towhich a saw blade 27 with facedown sawteeth is attached to the front endof a saber saw body held in a normal position. FIG. 2 shows anothercondition of a saber saw according to which the saw blade 27 isinversely attached to the saber saw body. However, the above-describedconventional saber saws of the orbital cutting type cannot operateproperly if saw blades are inversely attached to saber saw body as shownin FIG. 2.

The applicant's copending application Ser. No. 09/468,127 discloses asaber saw of the orbital cutting type which can operate properly evenwhen a saw blade is inversely attached to a plunger or a carrier.

PCT internal publication No. WO 98/07544 discloses a saber saw thatapproaches the better cutting performance of orbital saws without thecomplexity required for orbital motion and achieves a forward motion ofthe saw blade during the cutting stroke without resorting to orbitalmotion.

Preferred Embodiment

A preferred embodiment of the present invention will be explained withreference to FIGS. 3 to 18. Identical parts are denoted by the samereference numerals throughout the views. The directions used in thefollowing explanation are defined based on a saber saw held in a normalposition with a longitudinal axis extending in a horizontal direction.

Motor Section

An electrically driven motor 1 is accommodated in a resin-made motorhousing 2. A handle 3 is connected to the rear end of the motor housing2. The handle 3 is equipped with a switch 4 which allows a user toon-and-off control power supply to the electric motor 1.

Speed-reducing Mechanism

An inner cover 5, which is an aluminum product, is connected to thefront end of the motor housing 2. A gear cover 6, which is also analuminum product, is connected to the front end of the inner cover 5 foraccommodating a driving force transmitting mechanism which is describedlater. The electric motor 1 has a motor shaft 7 serving as a rotarymember outputting a rotational driving force of the electric motor 1. Adriving gear 8 is formed at the front end of the motor shaft 7. Asecondary shaft 9 is positioned in parallel with the motor shaft 7. Theinner cover 5 supports the front end of motor shaft 7 and the rear endof secondary shaft 9. A driven gear 10 is attached on the secondaryshaft 9 so as to mesh with the driving gear 8. The driving gear 8 andthe driven gear 10 cooperate as a speed reducing mechanism. Therotational force of electric motor 1 is transmitted to the secondaryshaft 9 via the speed reducing mechanism. The secondary shaft 9 rotatesat a reduced speed.

A first slant shaft portion 9 a is formed at the front end of thesecondary shaft 9. The first slant shaft portion 9 a inclines withrespect to the secondary shaft 9. A second slant shaft portion 9 b isformed at the rear end of the secondary shaft 9. The second slant shaftportion 9 b inclines with respect to the secondary shaft 9 so as to haveopposite phase relationship with respect to the first slant shaftportion 9 a. The first slant shaft portion 9 a and the second slantshaft portion 9 b cooperate to cause a plunger 20 and a counterweight 31to reciprocate in opposed directions with a phase difference of 180°.

A sub shaft 11 is attached to the front end of the secondary shaft 9.The sub shaft 11 is coaxial with the secondary shaft 9. The motorhousing 2, the inner cover 5, and the gear cover 6 cooperativelyconstitute a housing of the saber saw.

Reciprocating Shaft Supporting Structure

Two axle bolts 12 are opposed and coaxially attached to the front end ofthe gear cover 6. A guide sleeve 13 is hingedly supported at the innerends of the axle bolts 12 and is swingable about the common axis of theaxle bolts 12 (refer to FIG. 4). The common axis of the axle bolts 12serves as a pivot for allowing the guide sleeve 13 to swing in anup-and-down direction normal to a reciprocating direction of the plunger20. Two opposed rectangular through holes 14 are opened at the rear endof the guide sleeve 13. A change shaft 15 is rotatably installed on theinside wall of the inner cover 5. The change shaft 15 is inserted intothe rectangular through holes 14 (refer to FIG. 5). More specifically,the change shaft 15 has two symmetric flat surfaces 15 a formed atopposite sides of the central region thereof. The flat surfaces 15 aextend in a wider lateral region larger than the diameter of the guidesleeve 13. A change lever 16 is securely connected to the axial end ofthe change shaft 15. The change shaft 15 rotates in accordance with aturning operation of the change lever 16. The rotation of the changeshaft 15 selectively allows or restricts the swing motion of the guidesleeve 13 about the pivot thereof. FIG. 5 shows the guide sleeve 13which is released from restriction of the change shaft 15 and swingablewithin a predetermined angular range.

Rotation-Reciprocation Converting Mechanism (for Plunger)

A first wobble plate 18 has a sleevelike base portion coupled around thefirst slant shaft portion 9 a via two bearing rings 17. The first wobbleplate 18 has a swing shaft 18 a integrally extending from the sleevelikebase portion in a direction perpendicular to the axis of the first slantshaft portion 9 a. A ball portion 18 b is formed at the distal end ofthe swing shaft 18 a. A cylindrical bearing metal 19 is press fittedinto the front end portion of the cylindrical guide sleeve 13. Theplunger 20 reciprocates along the cylindrical inner wall of the bearingmetal 19. The plunger 20 has a larger-diameter portion 20 a at the rearend thereof. A slight clearance is provided between the larger-diameterportion 20 a and the cylindrical inner wall of the guide sleeve 13. Theswing shaft 18 a of the first wobble plate 18 is inserted into upper andlower openings formed on the larger-diameter portion 20 a of the plunger20. An upper opening 20 b of the larger-diameter portion 20 a is looselycoupled with the ball portion 18 b of the swing shaft 18 a. The ballportion 18 b can roll along the cylindrical edge of the upper opening 20b. The lower opening of the larger-diameter portion 20 a is so wide thatthe swing movement of the swing shaft 18 a is not blocked by the loweropening of the larger-diameter portion 20 a. With the above-describedarrangement, the rotational motion of the secondary shaft 9 is convertedinto reciprocative motion of the plunger 20.

Counterweight Holding Mechanism

The counterweight 31, supported by two guide shafts 33, reciprocates inthe same direction as that of the plunger 20. Each of the guide shafts33 has both ends fixedly supported by the inner cover 5 and the gearcover 6. The counterweight 31 is a sleevelike member surrounding theguide sleeve 13. The centroid of the counterweight 31 agrees with thatof the plunger 20 (refer to FIGS. 5 and 6).

Rotation-Reciprocation Converting Mechanism (for Counterweight)

A second wobble plate 32 has a sleevelike base portion coupled aroundthe second slant shaft portion 9 b via a single bearing ring 17. Thesecond wobble plate 32 has a swing shaft 32 a integrally extending fromthe sleevelike base portion in a direction perpendicular to the axis ofthe second slant shaft portion 9 b. A ball portion 32 b is formed at thedistal end of the swing shaft 32 a (refer to FIG. 3).

To avoid interference between the ball portion 18 b and the ball portion32 b, the swing shaft 32 a of the second wobble plate 32 is angularlyoffset by an offset angle α° with respect to the swing shaft 18 a of thefirst wobble plate 18 when seen from the axial end of the secondaryshaft 9 as shown in FIG. 7. The inclination angle of each of the firstslang shaft 9 a and the second slang shaft 9 b with respect to thesecondary shaft 9 is determined considering the offset angle α° so thatthe plunger 20 and the counterweight 31 can cause reciprocative motionsopposed to each other with a phase difference of 180°. Morespecifically, each inclination angle with respect to an axis of thedriven gear 10 is maximized at the position corresponding to the offsetangle α°. A bore 31 c, provided on the counterweight 31, is looselycoupled with the ball portion 32 b of the second wobble plate 32. Theball portion 32 b can roll along the cylindrical edge of the bore 31 c.With this arrangement, the rotational motion of the secondary shaft 9 isconverted into the reciprocative motion of the counterweight 31 (referto FIG. 7).

Vibration of the plunger 20 caused in its axial direction can becanceled by the reciprocative motion of the counterweight 31 when aproduct of mass and stroke of the counterweight 31 is identical withthat of the plunger 20.

Blade Attaching & Detaching Mechanism

A blade attaching portion 20 c is formed at the front end of the plunger20. The blade attaching portion 20 c comprises a slit 20 d into whichthe saw blade 27 is inserted and locked by a stepped blade locking pin30. Cylindrical blade holders 28 and 29 are provided around the bladeattaching portion 20 c. The blade holder 28 is axially shiftable towardthe rear end of the plunder 20 while it rotates against a resilientforce. The stepped blade locking pin 30 retracts in response to theaxially rearward and rotational movement of the blade holder 28. Thismechanism allows the user to insert the saw blade 27 into the slit 20 dwhen the user holds the blade holder 28 at the rearward position. Whenreleased, the blade holder 28 shifts in the axially forward directionand returns its home position while it rotates in the oppositedirection. With this returning motion, the stepped blade locking pin 30engages the saw blade 27 and firmly fixes the saw blade 27 in the slit20 d of the plunger 20. Regarding the direction of the saw blade 27,this blade holding mechanism allows the user to set the saw blade 27upside down when attaching it to the blade attaching portion 20 c of theplunger 20. The applicants' earlier U.S. patent application Ser. No.09/426,646 filed Oct. 25, 1999 discloses the more detailed structure forthe blade attaching and detaching mechanism.

Front Holding Structure

A resin-made front cover 24 partly covers the housing of the saber saw,i.e., the motor housing 2, the inner cover 5 and the gear cover 6. Abase 25 is attached to the front end of the gear cover 6 and isshiftable in the axial direction via a fixing lever 26. The base 25stabilizes the position of the saber saw with respect to a material 36to be cut by the saber saw.

Swing Sawing Mechanism

A roller shaft 21 is provided at the rear part of plunger 20 and looselycoupled in axially elongated holes 13 a opened on the guide sleeve 13.The roller shaft 21 has both ends rotatably supporting swing rollers 22thereabout. The axially elongated holes 13 a guide the roller shaft 21and the swing rollers 22 to reciprocate together with the plunger 20. Analtitudinal width of each elongated hole 13 a is slightly larger than adiameter of the roller shaft 21. The guide sleeve 13 and the rollershaft 21 cooperatively prevent the plunger 20 from rotating in thecircumferential direction, thereby providing an antiroll mechanism forthe saw blade 27.

Each of the swing rollers 22 is located between a pair of opposingsurfaces, i.e., lower track 31 a and upper track 31 b, of an axiallyelongated groove formed in the counterweight 31. These tracks 31 a and31 b extend in the axial direction of the plunger 20 with a longitudinallength longer than a sum of respective strokes of plunger 20 andcounterweight 31 (refer to FIGS. 7 and 8). To adjust a swing motion ofthe plunger 20, each of the lower track 31 a and the upper track 31 b isslightly inclined as shown in FIG. 8.

FIG. 8 shows the change shaft 15 allowing the guide sleeve 13 to swing.The plunger 20, coupled in the guide sleeve 13, is swingable about thecommon axis of the axle bolts 12. The swing rollers 22 roll on the lowertrack 31 a or the upper track 31 b of the counterweight 31. In thisrespect, the counterweight 31 not only cancels the axial vibration ofthe plunger 20 but restricts the swing motion of the guide sleeve 13 andthe plunger 20. According to this embodiment, the guide sleeve 13 andthe plunger 20 are swingable about the common axis of the axle bolts 12in both clockwise and counterclockwise directions in an angular range ofapproximately ±1.54° with respect to the swing center thereof as shownin FIG. 9.

As the guide sleeve 13 is engaged with the counterweight 31 via theswing rollers 22, there is no direct interference between the guidesleeve 13 and the counterweight 31. As shown in FIG. 9, the guide sleeve13 does not interfere with the inside wall of the counterweight 31 atthe uppermost position (as indicated by solid line). When the guidesleeve 13 is positioned at the lowermost position (as indicated by adotted line), no interference occurs as the lower part of thecounterweight 31 is widely opened (refer to FIG. 7).

Sawing Operation with Linear Reciprocative Motion FIGS. 10 to 12 showsawing operation of the saber saw in a condition where the change shaft15 locks the guide sleeve 13 to restrict the swing motion of the plunger20. In this case, the change shaft 15 is in an upright position wherethe flat surfaces 15 a of the change shaft 15 are substantiallyperpendicular to the axis of the guide sleeve 13. The upper and loweredges of the upright change shaft 15 are firmly engaged with therectangular through holes 14 of the guide sleeve 13. The change shaft 15inhibits swing motion of the guide sleeve 13 about the common axis ofthe of the axle bolts 12.

During sawing operation, a user applies a downward pressing force F1 tothe saw blade 27 via the saber saw body. As the swing motion of theguide sleeve 13 is inhibited in this condition, the swing rollers 22 arenot brought into contact with the track 31 a or 31 b of thecounterweight 31. As a result, the plunger 20 and the saw blade 27perform simple linear reciprocation. The simple linear reciprocation ofthe saw blade 27 is suitable for cutting a hard material such as a steelworkpiece which generates a great reaction force.

Orbital Sawing Operation with Facedown Saw Blade

FIGS. 13 to 15 show the saw blade 27 normally attached to the plunger 20with sawteeth facing downward. The saber saw is in a condition where thechange shaft 15 unlocks the guide sleeve 13 to allow the swing motion ofthe plunger 20. In this case, the change shaft 15 is in a lying positionwhere the flat surfaces 15 a of the change shaft 15 are substantiallyparallel to the axis of the guide sleeve 13. The change shaft 15 isreleased from restriction of the rectangular through holes 14 of theguide sleeve 13. The change shaft 15 allows swing motion of the guidesleeve 13 about the common axis of the of the axle bolts 12.

During sawing operation, a user applies a downward pressing force F1 tothe saw blade 27 via the saber saw body. The plunger 20 supporting thesaw blade 27 receives an upward reaction force from a material to be cutand swings clockwise about the common axis of the axle bolts 12. Theswing movement of the plunger 20 is transferred to the guide sleeve 13.The guide sleeve 13 lowers its rear end downward. The swing rollers 22are depressed against the lower track 31 a of the counterweight 31. Theswing rollers 22, rolling along the lower track 31 a, allow the guidesleeve 13 (together with the plunger 20) to reciprocate relative to thecounterweight 31. As shown in FIGS. 13 to 15, during reciprocating inthe axial direction, the guide sleeve 13 swings about the common axis ofthe axle bolts 12 in an angular range of 0.44° to 1.54°. As a result,the plunger 20 and the saw blade 27 perform orbital reciprocationaccording to which the saw blade 27 moves along an arc line as shown byan arrow in each of FIGS. 13 to 15. In this case, the counterweight 31and the plunger 20 reciprocate in opposite directions with a phasedifference of 180°. Thus, the axial vibration of the plunger 20 can becanceled by the counterweight 31.

Orbital Sawing Operation with Faceup Saw Blade

FIGS. 16 to 18 show the saw blade 27 inversely attached to the plunger20 with sawteeth facing downward in a condition where the saber saw isheld upside down by a user as shown in FIG. 2. The saber saw is in thecondition where the change shaft 15 unlocks the guide sleeve 13 to allowthe swing motion of the plunger 20. In this case, the change shaft 15 isin the lying position where the flat surfaces 15 a of the change shaft15 are substantially parallel to the axis of the guide sleeve 13. Thechange shaft 15 is released from restriction of the rectangular throughholes 14 of the guide sleeve 13. The change shaft 15 allows swing motionof the guide sleeve 13 about the common axis of the of the axle bolts12.

During sawing operation, a user applies a downward pressing force F2 tothe saw blade 27 via the saber saw body. The plunger 20 supporting thesaw blade 27 receives an upward reaction force from a material to be cutand swings clockwise about the common axis of the axle bolts 12. Theswing movement of the plunger 20 is transferred to the guide sleeve 13.The guide sleeve 13 lowers its rear end downward. The swing rollers 22are depressed against the other track 31 b of the counterweight 31. Theswing rollers 22, rolling along the track 31 b, allow the guide sleeve13 (together with the plunger 20) to reciprocate relative to thecounterweight 31. As shown in FIGS. 16 to 18, during reciprocating inthe axial direction, the guide sleeve 13 swings about the common axis ofthe axle bolts 12 in an angular range of 0.44° to 1.54°. As a result,the plunger 20 and the saw blade 27 perform orbital reciprocationaccording to which the saw blade 27 moves along an arc line as shown byan arrow in each of FIGS. 16 to 18. In this case, the counterweight 31and the plunger 20 reciprocate in opposite directions with a phasedifference of 180°. Thus, the axial vibration of the plunger 20 can becanceled by the counterweight 31.

This invention may be embodied in several forms without departing fromthe spirit of essential characteristics thereof. The present embodimentas described is therefore intended to be only illustrative and notrestrictive, since the scope of the invention is defined by the appendedclaims rather than by the description preceding them. All changes thatfall within the metes and bounds of the claims, or equivalents of suchmetes and bounds, are therefore intended to be embraced by the claims.

What is claimed is:
 1. A saber saw comprising: a housing foraccommodating a motor; a driven shaft rotatably supported by saidhousing and rotated by said motor; a plunger capable of reciprocativemotion with respect to said housing and having a front end to which asaw blade is attached; a first motion converting mechanism interposedbetween said driven shaft and said plunger for converting rotationalmotion of said driven shaft into the reciprocative motion of saidplunger; a counterweight causing reciprocative motion with respect tosaid housing; a second motion converting mechanism interposed betweensaid driven shaft and said counterweight for converting the rotationalmotion of said driven shaft into the reciprocative motion of saidcounterweight; and a pair of opposing tracks formed on saidcounterweight so as to extend in a direction substantially parallel to areciprocating direction of said plunger, so that guide means of saidplunger reciprocates along one of said opposing tracks formed on saidcounterweight while maintaining a clearance between said guide means andthe other of said opposing tracks.
 2. The saber saw in accordance withclaim 1, wherein a roller shaft is provided at a rear end of saidplunger so as to extend in a direction normal to said reciprocatingdirection of said plunger, and swing rollers serving as said guide meansare rotatably supported at both ends of said roller shaft so as to rollalong one of said opposing tracks formed on said counterweight.
 3. Thesaber saw in accordance with claim 2, wherein said pair of opposingtracks are formed in an axially elongated groove of said counterweightand said swing rollers interpose between said opposing tracks so as toleave a predetermined clearance.
 4. The saber saw in accordance withclaim 2, wherein said swing rollers are depressed on one of saidopposing tracks formed on said counterweight when said saw bladereceives a reaction force from a material to be cut during a cuttingoperation.
 5. A saber saw comprising: a housing for accommodating amotor; a driven shaft rotatably supported by said housing and rotated bysaid motor; a plunger capable of reciprocative motion with respect tosaid housing and having a front end to which a saw blade is attached; aguide sleeve holding said plunger and being hingedly supported about apivot fixed to said housing so that said guide sleeve can swing in adirection normal to a reciprocating direction of said plunger; a firstmotion converting mechanism interposed between said driven shaft andsaid plunger for converting rotational motion of said driven shaft intothe reciprocative motion of said plunger; a counterweight causingreciprocative motion with respect to said housing; a second motionconverting mechanism interposed between said driven shaft and saidcounterweight for converting the rotational motion of said driven shaftinto the reciprocative motion of said counterweight; a pair of opposingtracks formed on said counterweight and extending in a directionsubstantially parallel to a reciprocating direction of said plunger, sothat said plunger reciprocates along one of said opposing tracks formedon said counterweight; a roller shaft provided at a rear end of saidplunger so as to extend in a direction normal to said reciprocatingdirection of said plunger and inserted in an elongated hole opened onsaid guide sleeve; and swing rollers rotatably supported at both ends ofsaid roller shaft so as to roll along one of said opposing tracks formedon said counterweight while maintaining a clearance between each swingroller and the other of said opposing tracks.
 6. The saber saw inaccordance with claim 5, wherein said pair of opposing tracks are formedin an axially elongated groove of said counterweight and said swingrollers interpose between said opposing tracks so as to leave apredetermined clearance.
 7. The saber saw in accordance with claim 5,wherein said swing rollers are depressed on one of said tracks formed onsaid counterweight when said saw blade receives a reaction force from amaterial to be cut during a cutting operation.